The present invention relates to the attenuation and measurement of laser beam power. In particular, it relates to the attenuation and measurement of laser beam power at the end of a laser guide such as an articulated arm which is used for providing a laser beam to an area of medical or surgical treatment. Even more particularly, the present invention is directed to attenuating the laser beam power at the end of an articulated arm laser guide to the low power levels necessary for medical or surgical treatment while at the same time providing the ability to measure accurately the delivered laser power.
The present surgical technology, and in particular, CO.sub.2 laser technology, uses an articulated arm to deliver spatially coherent light from a laser to a focusing accessory or other beam delivery device located at the end of the arm. Most often the laser is capable of delivering power in excess of 50 watts to the input end of the arm.
In general, the typical laser has a useful dynamic range of from 5:1 to 10:1. This limits the laser power to between 5 and 10 watts before instabilities occur that result in unstable power delivery.
Many surgical procedures must be performed in the power range of 20 milliwatts to 2 watts requiring some means of low power control. Current methods employ beam splitters within the laser console; however, this method results in inaccurate delivery of power since the power is measured before transmission through the arm. In addition, power measurement 29 devices designed to detect power at the 50 watt level are not accurate at 20 milliwatts.
The inventor is aware of the following references which relate to the measurement or detection of laser power levels.
______________________________________ 4,459,986 - Karaki 4,556,875 - Ishiwatari 4,476,512 - Sunago et al 4,716,288 - Doi 4,711,526 - Hennings, et al 4,423,726 - Imagawa et al 4,564,012 - Shimada et al 4,627,435 - Hoskin 4,580,557 - Hertzmann ______________________________________
U.S. Pat. No. 4,459,986 to Karaki discloses a surgical laser system wherein an amount of energy of an output laser beam emanating from a distal end of a flexible light guide is measured by arranging a partial reflecting mirror having a reflection factor of about 99% and a transmissivity of about 1% at the last rotating joint portion of the light guide nearest to the distal end. A heat sink is applied onto a rear surface of the partial reflecting mirror and a thermocouple is arranged in contact with the heat sink to measure the temperature of the heat sink due to the transmitted energy. The output energy of the laser beam can be accurately measured by the thermocouple without being affected by a variation of the transmissivity of the light guide.
The '986 Karaki patent thus shows placement of a thermal sensor near the end of a light guide so that the amount of laser energy can be measured at the output. This reference does not, however, disclose or suggest the concept of attenuating the laser energy at the distal end of a laser guide so that low energy levels can be accurately delivered to the area of medical treatment.
U.S. Pat. No. 4,476,512 to Sunago et al is similar to the Karaki reference in that it discloses the use of a sensor element located near the distal end of a light fiber for monitoring the laser power at the distal end of the fiber. Again, however, there is no teaching or suggestion of attenuating laser power at the distal end of a light fiber.
U.S. Pat. No. 4,711,526 to Hennings, et al discloses an attenuating beam splitter. Two beams are produced by the beam splitter, a primary beam, and a secondary beam, the latter being a product of at least two internal reflections within the refractive element comprising the beam splitter. The secondary beam is used for aiming since the full power beam will travel along the same path as the attenuated beam after the refractive element is moved out of the path.
U.S. Pat. No. 4,564,012 to Shimada et al discloses a laser surgical device wherein a laser power meter is provided into which a laser handpiece is inserted in order to check if the output power of the laser coincides with the desired power setting.
U.S. Pat. No. 4,580,577 to Hertzmann is similar to the Shimada et al reference in that it discloses the use of a calibration pod for calibrating the output of the laser device.
U.S. Pat. No. 4,556,875 to Ishiwatari discloses a power monitoring system for an optical fiber wherein a light detector is disposed in a handpiece provided at the output end of the optical fiber.
U.S. Pat. No. 4,716,288 to Doi discloses a device for detecting defects in a transmitting fiber which operates on the principle of detecting the amount of light reflected from the exit face of the optical fiber.
U.S. Pat. No. 4,423,726 to Imagawa et al discloses a safety device for a laser ray guide in which a laser ray-receiving element is installed on the input side of a lens of a laser ray guide such that defects occurring in the laser ray guide can be detected by the energy reflected to the laser ray-receiving element.
U.S. Pat. No. 4,627,435 to Hoskin shows a surgical knife heated by a laser with a thermocouple disposed in the knife for control purposes.